The rare earths have atomic numbers from 57 (La) to 71 (Lu), and comprise the elements across which the 4f orbitals are filled: that is, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). They have atomic configurations [Xe]6s25d14fn or [Xe]6s24fn+1, with n varying from 0 for La to 14 for Lu. Their most common ionic charge state is 3+, with the 4f levels spanning the Fermi energy. They are the only stable elements with more than marginally filled f-shell electronic orbitals and, as a consequence, they are the elements with the largest spin and orbital moments. In ordered solids they contribute to the most strongly ferromagnetic materials, a contribution that has ensured their utility in technologies that require strong permanent magnets. Despite their name they are by no means rare, with the exception of promethium, which has no stable nuclear isotope.
The rare earth nitrides were first investigated in the 1960s, when technological developments overcame the problems faced in separating the chemically similar members of the rare earth series. The rare earth nitrides are almost all ferromagnetic with magnetic states that vary strongly across the series and coercive fields depending strongly on the growth conditions. For example, SmN is the only known near-zero-moment ferromagnetic semiconductor, with an enormous coercive field, and GdN has a coercive field some three orders of magnitude smaller. The rare earth nitrides show promise in applications as diverse as spintronics, infrared (IR) detectors, and as contacts to group III nitride semiconductor compounds.
Magnetoresistive random-access memory (MRAM) is a non-volatile random-access memory technology. Data in MRAM is stored by magnetic storage elements, while other RAM technologies typically store data as electric charge or current flows. The magnetic storage elements in MRAM are formed from two magnetic layers, each of which can hold a magnetic field, separated by a barrier layer. One magnetic layer is a permanent magnet set to a particular magnetic alignment. The other magnetic layer stores data by aligning to an external field. The element can then exist in different configurations, with either parallel or antiparallel magnetisation directions. The two magnetic configurations are then distinguished because the electrical resistance through an element with an insulating barrier layer, or the resistance along a metallic barrier layer, is smaller when the magnetic layers are aligned parallel.
The structure and operational principles of giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) magnetic field sensors are similar.
All of the existing devices, however, have metallic magnetic layers.
Accordingly, it is an object of the present invention to go some way to avoiding the above disadvantage; and/or to at least provide the public with a useful choice.
Other objects of the invention may become apparent from the following description which is given by way of example only.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date.